High-purity metals and high-purity metal alloys are increasingly important in a wide range of technology areas. One area of extreme importance for high-purity metals is semiconductor fabrication. For semiconductor constructions, metallic purity can significantly affect semiconductor device quality and functionality. Accordingly, since impurities present in a source material can determine its suitability for use in semiconductor fabrication it is increasingly important to develop technology for detecting and/or quantifying impurities present in source materials.
Physical vapor deposition (PVD) methods are used extensively for forming thin metal films over a variety of substrates, including but not limited to, semiconductive substrates during semiconductor fabrication. A diagrammatic view of a portion of an exemplary PVD apparatus 10 is shown in FIG. 1. Apparatus 10 includes a target assembly 12. The target assembly illustrated includes a backing plate 14 interfacing a PVD or “sputtering” target 16. Alternative assembly configurations (not shown) have an integral backing plate and target.
Typically, apparatus 10 will include a substrate holder 18 for supporting a substrate during a deposition event. A substrate 20, such as a semiconductive material wafer is provided to be spaced from target 16. A surface 17 of target 16 can be referred to as a sputtering surface. In operation, sputtered material 18 is displaced from surface 17 of the target and deposits onto surfaces within the sputtering chamber including the substrate, resulting in formation of a layer or thin film 22.
Sputtering utilizing system 10 is most commonly achieved with a vacuum chamber by, for example, DC magnetron sputtering or radio frequency (RF) sputtering.
Various materials including metals and alloys can be deposited using physical vapor deposition. Common target materials include, for example, aluminum, titanium, copper, tantalum, nickel, molybdenum, gold, silver, platinum and alloys thereof. Sputtering targets are typically made of high-purity materials. However, even minute particles or inclusions such as, for example, oxides or other nonmetallic impurities in the target material can affect the deposited film and can lead to defective or imperfect devices.
Conventional analysis of metallic materials such as PVD target materials for impurities such as oxides typically involves dissolution techniques where a small sample of material is dissolved in acid. The resulting solution is filtered to retain un-dissolved particles on the filter. The size and number of particles retained on the filter is then determined to ascertain the amount of impurity particles present in the metallic material. However, this conventional technique presents a number of problems. First, the particles agglomerate during the filtering process giving inaccurate size and number data. Second, the imaging system used to measure particles is limited to detecting particles having a size greater than about 2 microns. Third, the process is relatively labor and time intensive. Accordingly, it is desirable to develop alternative techniques for metallic material analysis.